In the evolution of semiconductor manufacturing techniques from a mystifying art to a highly cost-effective, sophisticated technology, a continuing engineering effort has been exerted on the simplification and automation of semiconductor chip packaging operations. Such packaging operations differ from semiconductor device processing steps in that the device processing steps are typically performed while the devices are still arrayed as integral portions of a unitary, relatively large wafer. In packaging operations, on the other hand, the devices are typically handled as individual devices or chips, in other words, as separate small portions formed by incremental division of such wafers.
In handling or bonding the chips in the course of packaging them to make completed components, manual handling of the individual chips is still not uncommon. Operators are commonly engaged in aligning the chips to bond sites on substrates, or aligning leads or contact pads with respect to reticles or alignment marks. Typically the devices are viewed through microscopes to perform such alignment operations. Since such manual alignment operations are both cumbersome and costly in terms of operator time, it is desirable to automate the alignment operations whenever possible.
U.S. Pat. No. 3,946,931 to Bahnck et al. discloses an apparatus for bonding an article to a substrate. Automatic alignment features shown in the patent are examples of recent progress made toward automating typical handling and alignment techniques. The apparatus described in the Bahnck et al. patent orients and centers beam-lead chips by a technique which uses what is known as a centering cavity. The cavity has the form of a truncated, inverted pyramid, with a square cross section which downwardly decreases in size. The upper opening of the cavity is wide enough to accommodate the lateral extent of beam-lead chips and any anticipated lateral deviation from a desired center as well as any expected angular misorientation with respect to a desired orientation.
U.S. Pat. No. 3,982,979 to Hentz et al. discloses in detail the function of the centering cavity. One of the beam-lead chips to be centered is placed onto a central and axially reciprocable pedestal. The pedestal may have, in addition, a vacuum provision for temporarily holding the chip. The chip starts to orient and center itself against the sloped sides of the cavity when the outer tips of the beam leads contact the sloped inner surfaces of the cavity. On a typical beam-lead integrated circuit chip, a plurality of the tips of the beam-leads terminate along straight lines parallel to each of the four edges of the chip. When the chip is centered and properly oriented, each line of lead tips is positioned adjacent to and typically in contact with a respective one of the sloped walls of the cavity.
It has been a long standing problem that the walls of such a cavity are unreliable for orienting a chip when the chip has only one lead extending from each edge of the chip. The tip of such a single lead fails to form a clearly defined termination line parallel to the respective edge of the chip to which the chip may be oriented. Even when a chip has two leads extending from one of the surfaces and only a single lead extending from one of the other edges of the chip, the tips of the leads being guided against the sloped surfaces of the inverted truncated pyramid have a tendency to rotate the chip randomly away from a desired orientation. Heretofore, beam-lead chips having four or fewer leads with only one lead extending from at least one edge have therefore been centered by manual techniques. These manual techniques have kept packaging costs of such chips higher than those of similar chips being packaged by automated alignment techniques.